The present invention relates to nickel based superalloys, particularly to nickel based single crystal superalloys, or particularly nickel based single crystal superalloys for use as turbine blades, turbine vanes, turbine seals and combustor components of gas turbine engines, but they may be used in internal combustion engines etc.
Nickel based single crystal superalloys have been developed to provide improved high temperature mechanical properties such as creep strength. However, there are many other important properties which need to be optimized to a high level in order for a nickel based single crystal superalloy to be acceptable for use in a gas turbine engine.
Other properties which need to be optimized are density, resistance to oxidation, resistance to corrosion, compatibility with protective coatings, heat treatment response and castability.
There are three generations of nickel based single crystal superalloys which differ by the amount of the key element rhenium. The first generation of nickel based single crystal superalloys contained no rhenium, examples of these are disclosed in published UK patent application nos. GB2039296A, GB2073774A, GB2105369A, GB2106138A and GB2151659A. The first generation of nickel based single crystal superalloys have densities of 7.9 to 8.7 gm per cm3. The second generation of nickel based single crystal superalloys contained about 3 wt % rhenium, examples of these are disclosed in published European patent application nos. EP0155827A and EP0208645A. The second generation of nickel based single crystal superalloys have densities of 8.7 to 8.9 gm cm 3. The second generation of nickel based single crystal superalloys have a benefit in creep strength capability of about 30xc2x0 C. over the first generation of nickel based single crystal superalloys. The third generation of nickel based single crystal superalloys contained about 6 wt % rhenium, examples of these are disclosed in U.S. Pat. No. 5,366,695 and U.S. Pat. No. 5,270,123 and published European patent application no. EP0848071A. The third generation of nickel based single crystal superalloys have densities of 8.9 to 9.1 gm per cm 3. The third generation of nickel based single crystal superalloys have a benefit in creep strength capability of about 30xc2x0 C. over the second generation of nickel based single crystal superalloys.
Thus it is seen that the increase in creep strength is to the detriment of the density and the cost of the superalloy. An increase in density of the turbine blades and turbine vanes makes the gas turbine engine heavier and also results in a requirement to make the turbine rotor disc stronger to carry the heavier turbine blades, which also results in an increase in the weight of the turbine rotor disc.
The turbine blades requiring the greatest creep strength are usually those in the first stage of uncooled turbine blades, and for these turbine blades a third generation nickel based single crystal superalloy is used. However, for turbine blades and turbine vanes which are cooled the requirements are different. The creep strength requirement is lower and hence creep properties similar to the second generation nickel based single crystal superalloy are 25 sufficient. It is often the case that these cooled turbine blades and turbine vanes are protected by a ceramic thermal barrier coating. A major concern with a ceramic thermal barrier coating is that the ceramic thermal barrier coating will spall prematurely during engine service. The adherence of a ceramic thermal barrier coating is influenced by many factors, but a major factor is the composition of the superalloy substrate on which the ceramic thermal barrier coating is deposited.
The present invention seeks to provide a novel nickel based single crystal superalloy which has creep properties and high temperature oxidation resistance similar to a second generation nickel based single crystal superalloy but has reduced density compared to a second generation nickel based single crystal superalloy and better compatibility with a ceramic thermal barrier coating than a second generation nickel based single crystal superalloy.
Accordingly, the present invention provides a nickel based single crystal superalloy comprising 3-11 wt % cobalt, 4.7-5.7 wt % chromium, 2.4-3.0 wt % molybdenum, 3.0-3.8 wt % tungsten, 3.0-3.8 wt % rhenium, 5.5-7.0 wt % aluminum, 5.0-6.0 wt % tantalum, 0.5-1.0 wt % niobium, 0-0.2 wt % hafnium, 0-150 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The nickel based single crystal superalloy may comprise 9-11 wt % cobalt, 5.1-5.4 wt % chromium, 2.6-2.9 wt % molybdenum, 3.2-3.5 wt % tungsten, 3.2-3.5 wt % rhenium, 6.05-6.3 wt % aluminum, 5.4-5.7 wt % tantalum, 0.7-0.9 wt % niobium, 0.07-0.12 wt % hafnium, 50-150 ppm carbon, 0-100 ppm yttrium, 0-100 ppm, lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
Preferably the nickel based single crystal superalloy comprises 3-5 wt % cobalt, 5.1-5.4 wt % chromium, 2.6-2.9 wt % molybdenum, 3.2-3.5 wt % tungsten, 3.2-3.5 wt % rhenium, 6.05-6.3 wt % aluminum, 5.4-5.7 wt % tantalum, 0.7-0.9 wt % niobium, 0.07-0.12 wt % hafnium, 50-150 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The nickel based single crystal superalloy may comprise 4 wt % cobalt, 5.2 wt % chromium, 2.7 wt % molybdenum, 3.35 wt % tungsten, 3.4 wt % rhenium, 6.2 wt % aluminum, 5.5 wt % tantalum, 0.8 wt % niobium, 0.1 wt % hafnium, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The nickel based single crystal superalloy may comprise 10 wt % cobalt, 5.2 wt % chromium, 2.7 wt % molybdenum, 3.35 wt % tungsten, 3.4 wt % rhenium, 6.2 wt % aluminum, 5.5 wt % tantalum, 0.8 wt % niobium, 0.1 wt % hafnium, 100 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0.5 ppm sulfur and the balance nickel plus incidental impurities.
The present invention also provides a cast single crystal nickel based superalloy article, the superalloy of the article comprising 3-11 wt % cobalt, 4.7-5.7 wt % chromium, 2.4-3.0 wt % molybdenum, 3.0-3.8 wt % tungsten, 3.0-3.8 wt % rhenium, 5.5-7.0 wt % aluminum, 5.0-6.0 wt % tantalum, 0.5-1.0 wt % niobium, 0-0.2 wt % hafnium, 0-150 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The cast single crystal nickel based superalloy article may comprise 9-11 wt % cobalt, 5.1-5.4 wt % chromium, 2.6-2.9 wt % molybdenum, 3.2-3.5 wt % tungsten, 3.2-3.5 wt % rhenium, 6.05-6.3 wt % aluminum, 5.4-5.7 wt % tantalum, 0.7-0.9 wt % niobium, 0.07-0.12 wt % hafnium, 50-150 ppm carbon, 0-100 ppm yttrium, 0-100 P.P.S. lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
Preferably the cast single crystal nickel based superalloy article comprises 3-5 wt % cobalt, 5.1-5.4 wt % chromium, 2.6-2.9 wt % molybdenum, 3.2-3.5 wt % tungsten, 3.2-3.5 wt % rhenium, 6.05-6.3 wt % aluminum, 5.4-5.7 wt % tantalum, 0.7-0.9 wt % niobium, 0.07-0.12 wt % hafnium, 50-150 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The cast single crystal nickel based superalloy article may comprise 4 wt % cobalt, 5.2 wt % chromium, 2.7 wt % molybdenum, 3.35 wt % tungsten, 3.4 wt % rhenium, 6.2 wt % aluminum, 5.5 wt % tantalum, 0.8 wt % niobium, 0.1 wt % hafnium, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0-5 ppm sulfur and the balance nickel plus incidental impurities.
The cast single crystal nickel based superalloy article may comprise 10 wt % cobalt, 5.2 wt % chromium, 2.7 wt % molybdenum, 3.35 wt % tungsten, 3.4 wt % rhenium, 6.2 wt % aluminum, 5.5 wt % tantalum, 0.8 wt % niobium, 0.1 wt % hafnium, 100 ppm carbon, 0-100 ppm yttrium, 0-100 ppm lanthanum, 0.5 ppm sulfur and the balance nickel plus incidental impurities.
The cast single crystal nickel based superalloy article may comprise at least one internal passage for the flow of cooling fluid.
The cast single crystal nickel based superalloy article may comprise a bond coating on the article and a ceramic thermal barrier coating on the bond coating. The bond coating may comprise a layer of alumina. The bond coating may comprise a layer comprising platinum enriched gamma prime phase and platinum enriched gamma phase.